1. Field of the Invention
The present invention relates to a shaft seal apparatus that seals the shaft of rotary equipment using gland packings.
2. Description of Prior Art
A known shaft seal apparatus of the sort to which the present invention relates is shown in FIG. 10. This example of the prior art comprises a cylindrical stuffing box 1, a plurality of gland packings 2, a first packing gland 3, and a second packing gland 4. The cylindrical stuffing box 1 is mounted around a rotating shaft 9 of a rotary equipment body 6, with the gland packings 2 placed side by side in the axial direction in a cylindrical sealed space 10 formed between the rotating shaft 9 and the stuffing box 1. Those gland packings 2 are pressed between the first packing gland 3 on the side of a sealed liquid region and the second packing gland 4 on an atmospheric region side. In that way, the rotating shaft 9 is sealed to isolate an inner sealed liquid region 7 of a rotary equipment from an atmospheric region 8.
As shown, the prior art apparatus has the stuffing box 1 formed integrally with the first packing gland 3, with the second packing gland 4 held movably in the axial direction by a screw bolt 28. The screw bolt 28 is secured to the stuffing box 1 and has a tightening nut 29 thereon. This tightening nut 29 is tightened to press the gland packings 2 against the first packing gland 3. The tightening of tightening nut 29 can be adjusted to properly regulate the pressure at which the gland packing are pressed.
The following problems are known with the prior art apparatus in which the stuffing box 1 is fixed to the rotary equipment body 6. That is, in case the rotating shaft 9 vibrates or goes eccentric, there will occur a change in the relative positions of the stuffing box 1 and the rotating shaft 9 in the axial direction or radial direction, with the result that proper shaft sealing cannot be maintained.
If the relative positions of the stuffing box 1 and the rotating shaft 9 change in the radial direction, that is, if the gap between the circumferential surfaces of the two parts 1 and 9 changes, the contact pressure with which the gland packings 2 are pressed against the rotating shaft 9 will be uneven in the circumferential direction. The contact pressure will fall where the gap between the circumferential surfaces increases and will rise where the gap decreases. In the area where the contact pressure decreases, there will be a decrease or failure in packing or sealing performance. And where the contact pressure increases, abnormal wear due to contacts between the gland packing 2 and the rotary shaft 9 will occur. In other words, the overall shaft sealing could deteriorate.
Another problem with the prior art is as follows. The prior art apparatus is built so that the tightening nut 29 is tightened to move the second packing gland 4 toward the first packing gland 3 formed integrally with the stuffing box 1, thus pressing the gland packings 2 against the first packing gland 3. That is, the pressing force by the second packing gland 4 successively propagates from the gland packings 2 on the atmospheric region side which the pressing force directly acts on toward the adjacent gland packings 2 on the sealed liquid region side. The tightening pressure which the gland packings 2 are subjected to (or compression in the axial direction of the gland packings 2) decreases toward the sealed liquid side. In turn, the contact pressure with which the gland packings 2 are pressed against the rotating shaft 9 (and the stuffing box 1), that is, the shaft sealing force P, falls toward the sealed liquid region side as shown in FIG. 11, with the shaft sealing force P of the gland packing closest to the sealed liquid region and engaged with the first packing gland 3 being lowest. That is not desirable for a shaft seal apparatus, an object of which is to seal the shaft from the sealed liquid region 7. In the case where the sealed liquid region 7 comes under a very high pressure or great pressure fluctuation, for example, a good and stable shaft sealing performance could not be expected from such a shaft seal apparatus.
The present invention addresses those problems with the prior art. It is an object of the present invention, therefore, to provide a shaft seal apparatus that allows gland packings to maintain a good and stable shaft sealing performance even when the shaft vibrates or goes eccentric.
To achieve the object of the present invention, the following two features are incorporated in a shaft scaling apparatus in which gland packings are placed in a cylindrical space formed between a rotating shaft and a stuffing box surrounding the outer circumferential surface of the rotating shaft; and gland packings are clamped by a first packing gland on a sealed liquid region side and a second packing gland on an atmospheric region side, to seal a shaft from a sealed liquid.
The first feature is that the first packing gland is fixed to a rotary equipment body while the second packing gland is fixed to the stuffing box; wherein a first packing tightening mechanism is provided between and connects the first packing gland and the stuffing box such that the first packing gland and the stuffing box are movable relative to one another within specific ranges in the axial and radial directions of the shaft and are urged in the axial direction and held at specific, relatively movable positions.
The second feature is that, with the first packing gland fixed to the rotary equipment body, the first packing tightening mechanism is provided between and connects the first packing gland and the stuffing box such that the first packing gland and the stuffing box are movable relative to one another within specific ranges in the axial and radial directions of the shaft and are urged in the axial direction and held at specific, relatively movable positions, while a second packing tightening mechanism is provided between and connects the second packing gland and the stuffing box such that the second packing gland and the stuffing box are movable relative to one another within specific ranges in the axial and radial directions of the shaft and are urged in the axial direction and held at specific, relatively movable positions.
With a shaft sealing apparatus of such construction, the gland packings placed between the stuff box and the rotating shaft would not change in shaft sealing performance even in cases of axial vibration, eccentricity, or the like, because the stuffing box moves along with the rotating shaft, and as a result there is no change in the relative positions of the two. It is further noted that the first packing gland on the sealed liquid region side is fixed to the rotary equipment body with the stuffing box connected to the first packing gland via the first packing tightening mechanism so that the first packing gland exerts pressure on the gland packings. Therefore, the gland packing closest to the sealed liquid region is the highest in tightening pressure or shaft sealing force. That helps the shaft sealing apparatus of the present invention maintain a good and stable shaft sealing performance, irrespective of the sealing conditions.
In a preferred embodiment, the first packing tightening mechanism comprises a screw bolt extending in the axial direction of the rotating shaft and fixed to the first packing gland, a through hole provided in the flange portion of the stuffing box, the through hole being larger by a specific amount than the screw bolt, a tightening nut engaging with a part of the screw bolt that is backward of and out of the through hole, and a compression coil spring located between the flange and the tightening nut. In another embodiment, the second packing tightening mechanism comprises a screw bolt extending in the axial direction of the rotating shaft and fixed to the stuffing box, a through hole provided in the flange portion of a second packing gland, the through hole being larger than the screw bolt by a specific amount, a tightening nut engaging with a part of the screw bolt that is backward of and out of the through hole, and a compression coil spring located between the flange and the tightening nut. It is desirable to have the stuffing box provided with a partition that divides the seal space into two seal compartments arranged side by side in the axial direction. Gland packings are placed in each seal compartment. It is also desirable that a free-sliding ring slidable in the sealed space in the axial direction be provided between the first packing gland and the gland packings in the seal space.